Battery management systems for improving battery efficiency in electric vehicles

Battery cost and battery capacity are key factors to determine whether or not electric vehicles would be used widely. Having a high energy density, lithium-ion battery can improve the mileage range of electric vehicles, yet the battery cost remains high. Although lead-acid battery has lower energy density than that of lithium-ion batteries, lead-acid battery cost less. Moreover, lithium-ion battery features an excellent discharge characteristic, whereas load current significantly impacts the capacity of lead-acid battery. This paper proposes a novel scheme to improve the efficiency of electric vehicle battery. In addition to connecting lead-acid battery with lithium-ion battery in parallel to the power supply, the proposed method combines their discharge characteristics to optimize the power management in order to improve the efficiency of battery and lower the cost of electric vehicle battery. The experimental result demonstrates that the available capacity can improve 30~50% of the rated capacity of the lead-acid battery. © 2010 WEVA.